it's a deliberate corruption of the ending (grammatically it's absolutely incorrect), but this is slang, used for kinda trying to sound cool, hardline. This could be used by somebody young and trying to look cool, for example, after a car crash an angry driver coming out of a car saying this to the other who had obviously been driving too fast, literally this is: "What the f.. are you doing, moth...er, going so fast!!"...
you will hardly be in a situation to use this)) to corrupt Russian endings the person will have to be born in a Russian speaking country.